Expression of neurotrophin receptors in vestibular nuclei during the postnatal development of the rat

Abstract

Neurotrophins and their receptors are known to play an important role in neuronal development. Postnatal development of neurons immunoreactive for three neurotrophin receptor tyrosine kinases (TrkA, TrkB, and TrkC) was examined in the rat vestibular nuclei and subnuclei. TrkA immunoreactivity was not observed in these areas during the first two postnatal weeks, though some TrkA-positive neurons were present in other vestibular-related brainstem regions (e.g. prepositus hypoglossal nucleus). In older rats (>P21), a strong immunostaining of TrkA was observed on both neuronal somata and nerve fibers within the lateral and spinal vestibular nuclei while no immunostaining was detected in the medial and superior vestibular nuclei and subnuclei. In the first few postnatal days, immunoreactivity for TrkB was virtually absent from the vestibular nuclei. At P4, a diffuse and very weak TrkB immunoreactivity was found restricted to cell bodies in the lateral and spinal vestibular nuclei as well as group y subnucleus. During the second postnatal week, the TrkB immunostaining became prominent throughout the vestibular nuclear complex. Extremely strong labelling was observed in the large-sized neurons. The intensity of TrkB immunostaining decreased to a moderate level at P21 and persisted until the adult stage. In contrast, immunoreactivity for TrkC within the vestibular nuclei was weak and diffuse during each of the postnatal ages studied. The differential expression pattern of these three neurotrophin receptors during development suggests a crucial role in the modulation of postnatal vestibular function.